Generally, most heat exchangers made of metallic material, such as an aluminum-containing metallic material, are so designed that their heat-dissipating and cooling portions have surface area as large as possible to enhance the heat-dissipating and cooling performance. In addition, the inter-fin space is extremely narrow to minimize the size of the heat exchanger. Therefore, when an evaporator is operated, moisture in the atmosphere condenses on the fin surface. The condensed water tends to form water drops which fill the fin gaps (clogging), when the hydrophilicity of the fin surface is poor. As a result, ventilation resistance is increased, which leads to reduction of the heat-exchanging efficiency. Such problems then arise as power loss, generation of noise, and the water drops scattering with the air stream to downstream side.
Several methods are therefore proposed and implemented for hydrophilization-treating the fin surfaces of a heat exchanger, so as to prevent water drops from filling the fin gaps and hence to improve the water wettability.
The methods for imparting hydrophilicity to the surface of metallic material are roughly classified into two types. One is an organic-inorganic composite type, in which an organic macromolecules are incorporated or added into an inorganic compound, particularly silica fine particles. The other method is an organic type mainly composed of an organic macromolecules free of silica.
For example, Japanese Examined Patent Publication (kokoku) No. 7-109355 discloses a heat exchanger, in which the former, composite organic-inorganic type is applied, and which comprises tubes and fins formed of aluminum. In this heat exchanger, a film is formed on a part or the entire surface of the aluminum and consists, at least in its surface, of a compound having a silanol group (—SiOH) and polyvinyl pyrrolidone. This film has excellent initial hydrophilicity. However, since its resistance to water solubility is poor, it is difficult to maintain the hydrophilicity for a long period of time. In addition, there remain problems unsolved with regard to foreign odor and lubricating property during the fin formation.
In addition, a hydrophilization agent for the heat exchanger disclosed in Japanese Unexamined Patent Publication (kokai) No.8-60031 contains water-dispersing silica (A), aqueous polyurethane resin (B), and an aqueous blocked polyurethane prepolymer (C). A hydrophilization method using this agent is disclosed. However, it cannot be said that the hydrophilicity persistence of the film is satisfactory.
Next, for example, Japanese Unexamined Patent Publication (kokai) No. 4-366182 is related to the latter organic type. It is disclosed that the hydrophilization surface-treating agent comprises, in terms of the solid matter, (a) 0.5˜6 parts by weight of polyvinyl pyrrolidone having 50˜1000 of polymerization degree, and (b) 1˜10 parts by weight of polyvinyl alcohol having 80% or more of saponification degree and 100˜1000 of polymerization degree, and further the agent has (a)/[(a)+(b)] in a range of 0.1˜0.9. A hydrophilization surface-treating bath and a hydrophilization surface-treating method, for which the hydrophilization surface-treating agent mentioned above is used, are disclosed. However, the corrosion resistance and the resistance of the film to solubility in water, formed by this treating agent are unsatisfactory.
In addition, Japanese Unexamined Patent Publication No. 6-322552 discloses an organic type with improved hydrophilicity and corrosion resistance, suppression of and foreign odor, that is, a hydrophilization surface treating agent, which contains 5˜50 parts by weight of polyacrylic acid and 5˜50 parts by weight of polyethylene oxide, based on 100 parts by weight of the composition, which consists, in terms of solid matter, 5˜25 parts by weight of sodium salt and/or potassium salt of carboxymethylcellulose, 25˜50 parts by weight of ammonium salt of carboxymethylcellulose, and 25˜70 parts by weight of N-methylolacrylamide. It is disclosed to use the hydrophilic surface-treating agent mentioned above for a hydrophilization surface-treating bath and a hydrophilization surface-treating method of aluminum material. The film formed by this method has poor hydrophilicity persistence.
As is described above, such hydrophilization agent which enables improved hydrophilicity persistence and corrosion resistance to be imparted to a heat exchanger has not been established at present.
The present invention solves the above-mentioned problems involved in the prior art. Specifically the present invention provides a hydrophilization agent, hydrophilization liquid, and hydrophilization method, which can impart improved hydrophilicity and corrosion resistance on the surface of metallic materials, the raw material of which is aluminum, aluminum alloy, copper, copper alloy, stainless steel and the like.